1. Field of the Invention
The present invention relates to vibrating means in a power drill, and more particularly to vibrating means which allows the power drill to selectively perform single operation of rotation only and composite operation of rotation and vibration for drilling.
2. Description of the Prior Art
The prior art vibrating means for use in a power drill comprises a spindle which is driven for rotation by a motor and is axially vibrated through sliding contact between the cam surface of a rotary cam fitted on the spindle and the cam surface of a fixed cam disposed in opposed relation to the rotary cam. In this case, however, as axial thrusting force applied to the spindle increases, the contact pressure between the two cam surfaces increases unlimitedly, and as the result, damping force is applied to the rotary cam, which, in turn, will result in remarkably increased load to the motor. Thus, the degree of loss of the driving energy for the spindle becomes excessive in comparison with the power of the spindle. In case the power supply for the motor is a battery, conspicuous consumption of the battery is a grave disadvantage.